Many polymeric, such as polypropylene and polyester, materials have many excellent properties, such as low specific weight, high strength and modulus, toughness, fatigue resistance, and good resistance against chemicals. However, such polymeric materials generally possess poor wettability, dying ability, bondability, adhesion to various matrices, etc. Therefore, for many applications, it is required or advantageous to treat the surface of endless elongated objects, such as filaments, before they are e.g. processed into a final product.
In industrial scale, the surface treatment is normally carried out by a wet chemical processing. The wet processing has some inherent disadvantages, such as it may negatively influence bulk properties of the treated material, the process is often environmentally detrimental because it uses a lot of harmful and/or toxic chemicals, it needs and pollutes a lot of water, and it is costly in both processing time and energy because the processing requires heating and drying. In addition, some wet deposition processes are difficult to scale-up due to complicated multi-step processing steps.
New plasma technologies, which are dry and environmentally friendly, have appeared recently. Plasma modification only takes place on the uppermost surface and does not change the bulk properties of the treated material when used appropriately. Although the laboratory-scale feasibility of plasma technologies for the treatment of elongated objects, such as filaments, has been shown, those technologies still have many drawbacks and no commercial plasma equipment for the continuous surface treatment of high volume endless filaments, and elongated objects in general, is available.
In a prior art pulsed surface discharge process (also called aborted arc), an endless fibre is guided through two hollow tubular on-axis-arranged electrodes, and plasma is generated between the electrodes. The generated plasma is rather intense. As the melting temperature of treated polymer fibres is quite low, usually below 200° C., the high intensity of plasma forces the treatment time to be very short, e.g. circa 0.1 second per 1.5 cm distance between the electrodes, in order to prevent the melting of the treated material. Moreover, the gas composition influences a path in which plasma channels develop—the plasma channel can bridge the discharge electrodes either through the gas environment, i.e. not touching the treated fibre, or along the surface of the fibre. For example, in a pure nitrogen atmosphere, plasma channels tend to spread on the surface of fibres but when oxygen is present, plasma channels rather bridge the electrodes through the gas atmosphere without touching, and thus treating, the fibre itself. Both the high intensity of plasma and the sensitivity of discharge to gas composition result in an inhomogeneous surface treatment. Inhomogeneity of the treatment with the aborted arc discharge is further enhanced by the diameter of the treated fibre—the larger diameter of a fibre the larger level of inhomogeneity. That is basically due to the fact that only one plasma channel occurs at one moment, i.e. plasma channels appear sequentially, one after another, and there are not two or more plasma channels present simultaneously.
It is noted that the earlier filed but non-published European patent application having application number 05076567.6 discloses a method for depositing a polymer layer containing nanomaterial on a flat substrate material, such as a textile, paper, foil, membranes, leather and/or ceramics, comprising the steps of providing the substrate material, providing a polymerization material near a surface of the substrate material, conducting a flow near the surface of the substrate material, the flow comprising a nanomaterial, and depositing the polymer layer containing nanomaterial on the surface of the substrate material by applying a plasma polymerization process.
The present invention is directed toward overcoming one or more of the problems discussed above.